It is generally accepted that the earth is fast approaching an energy crisis of incalculable proportions. Some say that crisis will occur around the year 2040.
It appears that solar power may be the only source that can theoretically overcome the upcoming energy crisis without disrupting energy costs. Geothermal energy is a distant second possibility, but clearly at much higher costs.
Solar energy is principally suited to mitigating such a future energy crisis. For instance, almost 10'000 GTEP (TEP=Tons Equivalent Petrol) of solar radiation reaches the earth every year. Yet, only up to 5 GTEP of usable solar power would be needed to make a significant step toward energy sustainability for the earth.
However, there have been practical limitations to large-scale implementation of energy producing systems that rely on the sun. For example, photovoltaic cells are capable of converting solar energy (i.e. sunlight) to usable energy, i.e. electricity. But the overall efficiency of these devices is about 10-18%, depending on the materials used. Also, higher efficiency generally requires more expensive materials. Still further, the manufacture of photovoltaic cells requires the use of highly toxic chemicals, which present a significant and ever-expanding environmental problem.
For these reasons, solar thermal technology, the other main technology for converting solar energy to electricity, seems to be the only potential solution for producing a sufficient number of GTEPs in the foreseeable future, while remaining relatively inexpensive.
A specific solar thermal technology that is now widely being used in pilot applications is the solar parabolic trough. A parabolic trough, shaped like the bottom half of a large drainpipe, reflects sunlight to a central receiver tube that runs above it. Pressurized water and other fluids are heated in the tube and used to generate steam, which can then drive turbo-generators to produce electricity or to provide heat energy for industry.
In theory, parabolic troughs have had the potential for efficient electricity production, because they can achieve relatively high turbine inlet temperatures. However, in practice the land requirements for this technology are significant. Moreover, recent studies indicate that previously estimated electricity costs, using this technology, may have been over-optimistic. In short, the perceived promise on this technology has not yet delivered tangible benefits, in a practical sense, either due to inefficiencies or excessive costs, and also due to the inherent limitations and variations in solar irradiation. More specifically, these trough collectors require expensive and maintenance-intensive guidance systems to dynamically adjust the angular positions of the panels of the trough, dependent on the sun's position. This requires expensive gear drives, and also large support structures that can withstand significant load fluctuations and other structural considerations.